The present invention relates to a removable adhesive sheet, more particularly to a removable adhesive sheet whose adhesion capability does not decline with a frequent repetition of bonding to and removing from various adherends.
A conventional adhesive sheet has generally been formed by coating the adhesive layer forming surface of a paper, a plastic or a metal substrate with an adhesive. However, in such a sheet, the adhesive layer forming surface has been coated smoothly all over with the adhesive, which, although permitting bonding of the sheet to an adherend, does not permit removal from and rebonding to that adherend (or to some other adherend) repeatedly. this is because, due to so-called face adhesion of the adhesive sheet to the adherend, the adherend is partially peeled off to cover the surface of the adhesive or conversely the adhesive partially remains on the adherend when the sheet is removed, resulting in the remarkable reduction of adhesive force of the adhesive sheet through repetition of bonding and removing thereof.
Therefore, various adhesive sheets have been developed in which a concept of so-called point adhesion, instead of face adhesion, is applied. For these sheets, removal is made possible by making uneven the surfaces of the adhesive layers or by other methods reducing the areas of the sheets which come into contact with adherends. Among such removable adhesive sheets, there are, for example, a sheet to which an adhesive is applied in lines or in dots (refer to Japanese Provisional Utility Model Publn. Nos. 67060/1973, 54546/1984 and 133641/1984), a sheet whose adhesive layer itself is formed unevenly (refer to Japanese Provisional Utility Model Publn. Nos. 17561/1975 and 44750/1984), and a sheet in which an uneven portion is formed on its substrate and an adhesive is applied thereto (refer to Japanese Provisional Utility Model Publn. Nos. 116453/1974 and 135474/78, Japanese Utility Model Publication Nos. 4460/1976 and 3396/1977; Japanese Provisional Utility Model Publication No. 45340/1983 and U.S. Pat. No. 3,386,846).
The above-described adhesive sheets can be bonded and removed repeatedly many times. In such adhesive sheets, however, the effective area capable of coming into contact with an adherend had been merely reduced for the purpose of facilitating the removal of the sheet, and hence the adhesive force thereof to an adherend has been insufficient. In addition, the adhesive itself, which is capable of coming into contact with the adherend at the protrusive portions of the uneven surfaces of the adhesive sheets, tends to be physically released, and therefore such adhesive sheets become unusable when they are bonded to and removed from an adherend only a few times.